The methodology presented in this paper is the result of accumulated experience gained through many years of developing several expert systems in the agricultural domain by the Central Laboratory for Agricultural Expert Systems (CLAES). We have adopted a spiral model for the overall life cycle of expert systems development. As will be explained in this paper, the development methodology of an expert system has two aspects: Knowledge engineering, and Software engineering. From the knowledge engineering aspect, we adopted the CommonKADS methodology, and model driven approach has been applied. From the software engineering aspect, there are four activities for expert system development: requirements specification, design, implementation, and testing. This paper will include a detailed specification of each of these activities. The internal organization of CLAES is planed to cope with the technical requirements for expert systems development. The workflow among participating teams is explained.